This invention relates generally to improvements in digital versatile disc systems and, more particularly, to an improved navigation system for digital versatile disc systems.
Digital versatile discs (DVDs) are information storage devices used for storing prerecorded audio information, movies and computer software. The storage and playback mechanism used in DVDs closely resembles the mechanism used in compact discs (CDs) and DVD players and software use the same laser technology as CD players. Briefly, both DVDs and CDs store information as a pattern of pits formed in a metallic substrate. The pit patterns form digital words and can be read by shining a laser beam on the disc surface and detecting the reflected beam. However, the information storage capacity of a typical DVD is much higher than a CD. Presently available DVDs have a variety of capacities which depend on the technology used to manufacture the discs. Single-layer technologies can be either single or double-sided with capacities of 4.7 gigabytes and 9.4 gigabytes, respectively. Dual layer technologies will soon be available which use single or double sided capacities that hold approximately 8.5 gigabytes per side. This high information storage capacity makes DVDs suitable for storing not only audio information, but also video information and large amounts of computer data as well.
DVD players have many CD player features, such as the ability to play selections in any order desired and the ability to read information from any point on the disc. However, DVDs can store information in several formats. For example, DVDs which are used to store video information (hereinafter called DVD-VIDEO discs) may use various known information compression algorithms, such as MPEG-2 for video compression/decompression. A DVD may also include high fidelity sound as well. In addition, a DVD may also store uncompressed linear pulse code modulated data streams which have sample rates between 48-90 kHz and are sampled at 16 or 24 bits. Still other DVD versions (hereinafter called DVD-ROM discs) can store digital data for computer use, and the data may also be compressed on these discs.
Although DVD-ROM and DVD-VIDEO discs share compression algorithms, the data format on DVD-VIDEO discs is significantly different than the data format found on DVD-ROM discs. One important difference is that the data content on DVD-ROM is platform-specific, while DVD-VIDEO discs operate with a platform independent navigation engine for playing interactive movies. This navigation engine requires that the files on the DVD-VIDEO disc be referenced in predetermined directory structure.
In particular, each DVD-VIDEO disc contains a main directory denoted as a VIDEO_TS directory which contains two types of files distinguished with the file extensions .IFO and .VOB. During playback, these files are sorted by a DVD video player to form video xe2x80x9ctitlexe2x80x9d sets, which are groupings of all files necessary to play a particular DVD video xe2x80x9ctitlexe2x80x9d, for example, a movie. Each video title set is composed of one .IFO file and one or more .VOB files.
A file with the .VOB extension contains the actual multimedia data and is called a video object set. The location and format of the multimedia data stored in the video object set is defined by the associated .IFO file. In particular, .IFO files contain navigational data structures and a processor-independent interpreted language which specifies how the data structures are arranged.
The data structures themselves are composed of various objects called xe2x80x9cprogram chain objectsxe2x80x9d, xe2x80x9cprogram objectsxe2x80x9d, and xe2x80x9ccell objectsxe2x80x9d. Program chain objects link related program objects (or particular scenes) within a title and their data structures govern the playback of the program objects. For example, a simple title may contain only one program chain. However, complex titles may contain two or more program chains to allow random access to a variety of programs. The multiple program chain title can play programs linearly, randomly or in a xe2x80x9cshufflexe2x80x9d mode.
Each program object in a program chain is composed of elements called xe2x80x9ccell objectsxe2x80x9d. These objects instruct a DVD player which portion of the multimedia data in one of the .VOB files to decode. In particular, the data structures in a cell object are defined in the .IFO file and the multimedia content is found in one of the .VOB files. Each cell object directs the DVD player to begin playback at a specific location in the .VOB file which is referred to as a video object unit or xe2x80x9cVOBUxe2x80x9d. A VOBU is a container object that includes both navigational data as well as multimedia data.
Navigational input can also be obtained directly from a user by means of navigational buttons which are displayed under playback program control onscreen along with the multimedia data. The playback program controls both the time duration that the button appears on the screen and the manner that the system responds to the selection of a button by a user. For example, user selection of a button may cause the playback program to jump to a new location on the disk and begin playback at the new location.
The specific navigational commands which are recognized by a DVD player are controlled by a device independent language and a set of DVD player parameters which define the current state of the DVD player. These navigational commands can be broken into several categories including the following: Set, SetSystem, GoTo, Link, Jump and Compare.
Set commands permit primitive operations, such as compare or assignment operations, to manipulate the values of selected stored parameters. SetSystem commands are used to set the internal system parameters of the player. GoTo commands are used to skip to a specific instruction number in the instruction stream and Link and Jump commands cause program execution to jump to various locations within a title or menu on the disc. Finally, Compare commands allow value testing on either a system or user parameter.
The aforementioned DVD navigation commands provide an efficient way to move to different locations on the DVD under program control. However, prior art DVD navigation programs allow only one action to be taken at any given time. Consequently, these navigation programs cannot take advantage of features in modern operating systems such as WINDOWS 95(copyright), WINDOWS NT(copyright) or UNIX. For example, conventional DVD navigation systems which receive navigation commands during a data read operation from the DVD drive must wait for the data read operation to finish before processing the additional navigational commands. In addition, prior art navigation operations cannot be easily interrupted by user input. For example, a request to change to a different title, which request is received during DVD navigation, will generally be ignored by conventional systems.
Such prior art systems cannot perform simultaneous execution of multiple navigation commands. Instead, the commands must be performed serially. Further, such systems cannot perform content look ahead, in other words, read information associated with an upcoming title while a current title is being processed.
Therefore, there is a need for a DVD navigation system which if versatile and flexible and can take advantage of features in conventional operating systems.
The foregoing need is satisfied in one embodiment of the present invention in which a DVD navigation system is comprised of multiple synchronized threads. Each of the threads performs a single task so that several tasks can be performed concurrently.
In one embodiment, a stream parser thread, a navigation thread and a user interface thread are always created when the DVD player begins operation. In addition, a highlight thread may also be created if the DVD data stream contains highlight information. The stream parser thread receives the DVD data stream and extracts navigation commands and DVD content data from the stream. The navigation commands are sent to the navigation thread for processing, but the content data is sent to system decoders for video and audio decoding.
The navigation thread operates independently from the stream parser thread and processes the retrieved navigation commands to select portions of the DVD data stream for display. The user interface thread also operates independently from the stream parser thread and the navigation thread and responds to user commands generated by a user input device, such as a mouse or keyboard, for highlighting buttons on the DVD display screen.
Although the stream parser thread and the navigation thread operate independently, they are synchronized by means of an event control mechanism which may be part of the conventional operating system. Each thread controls an event semaphore and blocks on the semaphore controlled by the other thread.
The threads also share data structures which are protected by locks. Information can be passed between threads by means of objects which are created during thread operation.